Electric spark discharge device



G. W. SHOOBERT ELECTRIC SPARK DIS CHARGE DEVICE March 2, 1954- 2 Sheets-Sheet 1 Filed Feb. 12, 1952 March 2, 1954 G. w. SHOOBERT 2,671,186 ELECTRIC SPARK DISCHARGE DEVICE Filed Feb. 12, 1952 2 Sheets-Sheet 2 /0 VP f the drawback that in time fuel so that eventually the electrode never Patented Mar. 2, 1954 2,671,186 ELECTRIC SPARK DISCHARGE DEVICE George William Shoobert,

signor to K. L. G. don, England,

London, England, as-

Sparking Plugs Limited, Lona British company Application February 12, 1952, Serial No. 271,100 Claims. (Cl. 317-83) This invention relates to electric spark discharge devices such as are used for igniting inflammable mixtures in an after burner of a gas turbine engine. In the after burner of a gas turbine engine, the spark is usually required near the centre of a large diameter duct in which a fuel bearing gas flows. It has been proposed, for providing an ignition spark at the centre of a duct of an after burner to employ an electric spark discharge device which is of normal construction in that it has a central electrode surrounded for the whole of its length by a ceramic insulator which, in turn, was surrounded by a metal sheath.

In this proposal the ceramic insulator is made up of a number of separable lengths. However, such electric spark discharge devices suffered from (usually paraffin) found its way into the sheath and was deposited on the insulator or insulators where it was carbonised and provided a conducting path the electrode of the device and the earthed sheath became charged sufiiciently to cause a spark to jump across the spark gap.

The object of the present invention is to provide an electric spark discharge device suitable for extending across a large diameter duct and which does not suffer from this drawback.

Two electrical spark discharge devices constructed in accordance with the present invention and suitable for igniting a combustible mixture in a jet pipe of a gas-turbine engine will now be described with reference to the accompanying drawings, of which:

Figure 1 shows one device with the top half in section,

Figure 2 shows the other device with the top half in section, and Y '2 g Figure 3 shows the way in which the deviceis mounted in the jet pipe.

Referring to Figure 1, the discharge portion of the device comprises an elongated inner electrode member #0 which is provided at its discharge end with a discharge tip I l of rather smaller diameter but coaxial with it. remote from the discharge trode member iii is attached to a 1". gen erally cylindrical metal part 52, of rather greater diameter, which has an external thread it over part of its length. 1

A ceramic insulating member id is provided which is bored throughout its length and at one end is threaded to co-operate with the thread l3 but elsewhere fits the electrode ill or the discharge tip II which projects between from the end of the .i to the insulator. The electrode It is provided with an annular groove and the space. so formed, together with spaces surrounding the discharge tip adjacent the end of the electrode and surrounding the electrode adjacent the end of the metallic member 52, are filled with vitrous cementing material to provide seals l5, l6 and I1 sealing the ceramic insulator to the electrode structure. A metallic sheath i3 is provided which is secured insulator by being swaged over a flange at the middle of the insulator. The portion of the insulator which surrounds the metallic member H3 projects from the sheath l8 and is uncovered. The sheath i8 is shaped at [9 to provide, with the discharge tip II an electric spark gap.

The terminal portion device has an inner metallic member 28, and a cylindrical metal part of rather greater diameter to which the inner member it is attached, an insulator 22 and a metallic cover sleeve 23. This part of the structure of the terminal portion is arranged and connected togeth r similarly to that of the discharge portion, with the end of the insulator 22 which surrounds the cylindrical metallic member 2! projecting uncovered from the cover sleeve 23.

The cover sleeve 23 is formed with a spherical seating 2 5 and also provides a bore 25 which can receive a screened H. T. cable of which the core can be connected to the terminal end 26 of the inner member 20.

The two cylindrical metallic parts 2! and I2, the one in the terminal portion and the other in the discharge portion, are electrically connected together by a metal rod 30 which is bare and to which the cylindrical parts are welded.

The embodiment shown in Figure 2 is similar to that shown in Figure l in that it comprises a discharge portion having a central inner electrode member Alt, joined at one end to. a cylindrical metal part 45, an insulator 42 and a metal sheath it which shaped to constitute a spark with the discharge end of the inner electrode member iii. However, the cylindrical metal part 55 is provided with a head 4? which is locked against rotation with respect to the insulator 42 by a locking washer 44 which is deformed at 45 to enter a radial groove in the insulator. The head All is provided at its end remote from the inner electrode member to with a spherical hearing surface it.

The device shown in Figure 2 is also similar to that shown in Figure 1 in that it comprises a terminal portion having an inner metallic memher it connected to a cylindrical metal part 5| and surrounded by a ceramic insulator 52 to which is attached a cover sleeve 53 provided with a spherical seat 54.

In this embodiment, however, the metallic connector between the ends of the inner members 4| instead of being a metal rod, is tele scopic and comprises a metal tube 60 attached to the end of the inner member 5| by means of a spigot 6| to which it is welded. The tube is locked against rotation with respect to the insulator 52 by a washer 62 which is deformed at 63 to enter a radial groove in the end of the insulator.

The telescopic metallic connector also comprises a metal rod 65 which at one end is connected to the inner member 4| of the discharge portion by means of a spherical seat 56 which seats on spherical surface 46. The rod 65 slides in the tube 60 but is maintained in electrical contact therewith by the head 61 on the end of the rod 65 remote from the discharge portion and by the locking means 68 by which the tube and rod can be locked together.

This locking means comprises a split collet 10, the tapering surface of which co-operates with a tapering bore in one end of a nut member H the other end of which is threaded to co-operate with a thread 12 secured on the end of the tube 6! A locking nut 13 is also mounted on the thread 12.

Figure 3 shows how the embodiment illustrated in Figure 1 is mounted in the jet pipe of a gas turbine engine so as to ignite fuel injected through an auxiliary after burner jet. In Figure 3 the jet pipe is referenced B0 and is provided with a spherical socket 8i which receives the spherical seating 24 of the terminal portion of the device. The seating is retained in place by the lock nut 82. In the centre of the jet pipe 80 there is an auxiliary jet 83 for introducing fuel into the after burner stage and this jet is provided with a baffle 84.

The discharge portion of the device is mounted in a pocket 85 in the baffle 84 so that the spark will ignite the fuel discharged through the auxiliary jet.

The auxiliary jet and baffie are, of course 1ocated with respect to the jet pipe 80 and provide an earthing structure for the sheath l8 of the discharge portion.

It will be appreciated that the uncovered ends .1

of the insulators l4 and 22, which project beyond the sheath l8 and cover sleeve 23 respec tively, and also the base metal rod 30, are in use, located in the gas flow through the jet pipe.

This gas flow scours the surface of these parts and therefore prevents any carbon being deposited on the insulators 22 and I4. In this way the risk of a conductive path of carbon between the electrode and its earthed sheath being formed is eliminated.

It will be appreciated that the provision of ture at an angle to the remainder of the device.

The above description is not intended to limit the invention in any way and a number of modifications will be apparent to those skilled in the art which may be introduced without departing from the scope of the invention.

I claim:

1. An electrical spark discharge device comprising in combination a discharge portion having an elongated inner electrode member, an outer metallic sheath, and an insulating member separating said inner member and said sheath,-said inner member, sheath and insulating member being so shaped and arranged that an electric discharge can take place between one end of the inner member and the adjacent end of the sheath and that the insulating member projects uncovered from the other end or the sheath; a terminal portion having an elongated inner metallic member, an outer metallic cover sleeve, and an insulating member separating said inner member and said cover sleeve, said inner member, cover sleeve and insulating member of said terminal portion being so shaped and arranged that one end of the inner member is engageable with a suitable electric lead; and a metallic connector joining the ends of said two inner membersremote from their discharge and lead ends respectively, said metallic connector comprising a metallic tube attached and electrically connected to one of said inner members, a metallic rod attached and electrically connected to the other of said inner members and telescopically received in said tube, and locking means between said tube and said rod.

2. An electrical spark discharge device according to claim 1 wherein the tube is attached to the inner member of the terminal portion and the rod is attached to the inner member of the discharge portion.

3. An electrical spark discharge device according to claim 1 wherein the locking means comprises a split collet surrounding the rod, a screw thread formed on or secured to the tube, and a nut member having a tapered bore to co-operate with the collet and a threaded bore to co-operate with the screw thread, and a lock nut on the screw thread.

4. An electrical spark discharge device according to claim 1 further comprising a supporting structure for said terminal portion; a spherical socket in said supporting structure; and a spherical seating on said cover sleeve of said terminal portion received in said spherical socket.

5. An electrical spark discharge device according to claim 1 further comprising a spherical socket in the end of said inner member of said discharge portion remote from its discharge end; and a spherical seating on the adjacent end of said metallic connector received within, said socket.

' GEORGE WILLIAM SHOOBERT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,403,860 Heath July 9, 1946 2,508,420 Bedding May 23, 1950 2,566,373 Redding Sept. 4, 1951 2,604,510 Berkey July 22, 1952 

